Variable Displacement Compressor

Abstract

Overpressure of refrigerant in a refrigerant circuit is avoided. A swash plate type variable displacement compressor includes a muffler (muffler space 123 ) at the top of a cylinder block 101 thereof. The muffler space 123 is connected to a communication passage communicating with a discharge chamber of the compressor, and in this connecting portion, a check valve 200 for suppressing a backflow of the refrigerant is provided. The muffler space 123 communicates with a discharge-side external refrigerant circuit via a discharge port. An inlet port of the high-pressure relief valve 250 in the muffler space 123 communicates with the muffler space 123 located on downstream side of the check valve 200 , and an outlet port thereof communicates with a crank chamber 105 of the compressor through communication passages 101 c and 101 d of the cylinder block 101 . The crank chamber 105 communicates with a suction chamber of the compressor through a gas bleeding passage. The high-pressure relief valve 250 is opened when pressure in the muffler space 123 increases to overpressure to flow refrigerant at a high pressure into the crank space 105 from the muffler space 123 through the communication chambers 101 c and 101 d.

1 . A variable displacement compressor comprising:
 a housing including a plurality of cylinder bores formed in parallel with one another around a shaft, a crank chamber provided at the front thereof, a suction chamber and a discharge chamber provided at the rear thereof, a discharge passage connecting the discharge chamber to a discharge-side external refrigerant circuit, and a suction passage connecting the suction chamber to a suction-side external refrigerant circuit;   a piston inserted into the cylinder bore to reciprocate therein and compressing refrigerant drawn from the suction chamber to discharge the refrigerant into the discharge chamber;   a driving shaft rotatably supported in the housing;   a conversion mechanism including a swash plate of which inclination is changeable, the swash plate being arranged in the crank chamber and converting a rotary motion of the driving shaft into a reciprocating motion of the piston; and   a displacement control valve changing the inclination of the swash plate by controlling pressure in the crank chamber to change a stroke of the reciprocating motion of the piston,   wherein the housing includes a first pressure release passage branched from the discharge passage and connected to the crank chamber, and a second pressure release passage connecting the crank chamber to the suction chamber,   wherein a check valve that suppresses a backward flow of the refrigerant from the discharge-side external refrigerant circuit to the discharge chamber is provided in the discharge passage on an upstream side of a branching position at which the first pressure release passage branches off, and   wherein a high-pressure relief valve that opens the first pressure release passage when pressure in the discharge passage on a downstream side of the check valve exceeds a predetermined value is provided in the first pressure release passage.   
     
     
         2 . The variable displacement compressor according to  claim 1 , wherein at least part of the first pressure release passage is positioned radially outward of the cylinder bore seeing from the driving shaft, and the high-pressure relief valve is arranged at the at least part of the first pressure release passage. 
     
     
         3 . The variable displacement compressor according to  claim 1 , wherein the discharge passage includes a muffler having an extended space, and the high-pressure relief valve is arranged in the expanded space. 
     
     
         4 . The variable displacement compressor according to  claim 3 , wherein the muffler includes a volume part which is a part of the housing and is provided by forming a concavity on an external surface of a cylinder block in which the cylinder bore is formed, and a lid member which is a part of the housing and covers an opening of the volume part. 
     
     
         5 . The variable displacement compressor according to  claim 4 , wherein the high-pressure relief valve is clamped by the cylinder block and the lid member. 
     
     
         6 . The variable displacement compressor according to  claim 1 , wherein a low-pressure relief valve that opens the second pressure release passage when a pressure difference between the crank chamber and the suction chamber exceeds a predetermined value is provided in the second pressure release passage.